The field of this disclosure generally relates to electrolyte material for use in thermal batteries and, particularly, to ternary or quaternary electrolyte material that is substantially binder-free. The disclosure also relates to composites of electrodes and electrolytes that contain the electrolyte material and cathode and/or anode material and to batteries that contain the electrolyte material.
Thermal batteries tend to have relatively long shelf lives, high energy densities, require relatively low maintenance, and can withstand relatively high temperatures. Thermal batteries also tend to provide a short burst of power over a relatively short period of time. The burst may range from less than a second to an hour or more, with power typically ranging from about a watt or less to kilowatts. Such properties make thermal batteries suitable for military (e.g., batteries for missile guidance systems) and space exploration applications. Thermal batteries may also be used in other applications, such as in electric vehicles.
A typical thermal battery includes an anode, a cathode, an electrolyte-separator containing a solid electrolyte that is non-conductive at ambient temperature, and a pyrotechnic material (e.g., heat pellet as in FIG. 1 which may contain, for example, Fe—KClO4 powder) that provides a heat source to the battery. When battery operation is desired, an external stimulus is applied to the battery. For example, an electrical current may be applied to the battery to set off an electric match or an electro-active squib or a mechanical force (e.g., mechanical shock) may be applied to set off a concussion primer. The external stimulus causes the pyrotechnic material to ignite and begin to heat. Heat produced from the pyrotechnic material causes the previously solid electrolyte to melt and become conductive, which allows the battery to provide power for a desired application.
The anodes of thermal batteries are generally formed of an alkali or alkaline earth metal or alloy. A typical anode includes lithium metal or a lithium alloy, such as lithium aluminum, lithium silicon, or lithium boron.
Electrolytes for use with thermal batteries often include a eutectic mixture (i.e., a mixture which melts at a temperature lower than each of the individual components) of lithium chloride and potassium chloride and a binder, such as MgO, fumed silica or kaolin), which assists in containing the electrolyte within the thermal battery assembly upon melting, such as by capillary action, surface tension, or both. With typical thermal battery electrolytes, without sufficient binder, the electrolyte material may disperse throughout the battery, causing undesired shunts or short circuits in the cell. Unfortunately, the binder materials tend to be relatively resistant to ionic conduction and thus inclusion of the binder increases the impedance of the battery.
Cathode material for thermal batteries may vary in accordance with a variety of design parameters and generally includes a metal oxide or metal sulfide. By way of example, iron oxide (FeO4), iron disulfide (FeS2) or cobalt (CoS2) disulfide are often used as cathode material.
Thermal batteries are often formed using pellet techniques, such that each of the electrolyte, cathode, and heat source are formed into a wafer. In this case, the respective cell component chemicals are processed into powders and the powders are pressed together to form the cell. Each component may be formed as a discrete part, or the anode and/or cathode may include (i.e., be flooded with) electrolyte material to improve the conductivity of the cell.
Although conventionally-used electrolyte material (including cathodes or anodes that contain such electrolyte material and including batteries that include the electrolyte material) work relatively well, the binder adds undesired impedance to the cell. Accordingly, there is a continuing need for thermal battery electrolyte material that allows the amount of binder present in the material to be reduced or even eliminated but yet prevents the electrolyte material from dispersing to portions of the cell that may result in shunts or short-circuits. A continuing need also exists for battery components and batteries that incorporate such electrolyte material.